WO2018044089A1

WO2018044089A1 - Method and device for processing video signal

Info

Publication number: WO2018044089A1
Application number: PCT/KR2017/009527
Authority: WO
Inventors: 이배근
Original assignee: 주식회사 케이티
Priority date: 2016-08-31
Filing date: 2017-08-31
Publication date: 2018-03-08
Also published as: US20210076041A1; CN116939200A; CN116962679A; CN109691112A; ES2711223A2; KR102424420B1; KR20180025285A; EP3509307A4; CN117041538A; CN117014603A; US20210112251A1; CN109691112B; US20190200020A1; ES2711223R1; EP3509307A1; CN116980592A; US11451781B2; US11457218B2; US10841587B2; US20210105480A1

Abstract

A method for decoding an image according to the present invention may comprise: a step of inducing a reference sample of a current block; a step of determining an intra-prediction mode of the current block; and a step of obtaining a prediction sample of the current block by using the reference sample and the intra-prediction mode.

Description

Video signal processing method and apparatus

The present invention relates to a video signal processing method and apparatus.

Recently, the demand for high resolution and high quality images such as high definition (HD) and ultra high definition (UHD) images is increasing in various applications. As the video data becomes higher resolution and higher quality, the amount of data increases relative to the existing video data. Therefore, when the video data is transmitted or stored using a medium such as a conventional wired / wireless broadband line, The storage cost will increase. High efficiency image compression techniques can be used to solve these problems caused by high resolution and high quality image data.

An inter-screen prediction technique for predicting pixel values included in the current picture from a picture before or after the current picture using an image compression technique, an intra prediction technique for predicting pixel values included in a current picture using pixel information in the current picture, Various techniques exist, such as an entropy encoding technique for allocating a short code to a high frequency of appearance and a long code to a low frequency of appearance, and the image data can be effectively compressed and transmitted or stored.

Meanwhile, as the demand for high resolution video increases, the demand for stereoscopic video content also increases as a new video service. There is a discussion about a video compression technology for effectively providing high resolution and ultra high resolution stereoscopic image contents.

An object of the present invention is to provide a method and apparatus for efficiently performing intra prediction on an encoding / decoding target block in encoding / decoding a video signal.

An object of the present invention is to provide a method and apparatus for deriving a new reference sample based on pre-derived reference samples under a planner mode in encoding / decoding a video signal.

An object of the present invention is to provide a method and apparatus for deriving a predictive sample based on a weighted sum of a plurality of reference samples in encoding / decoding a video signal.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

The video signal decoding method and apparatus according to the present invention derive a reference sample for a current block, determine an intra prediction mode of the current block, and use the reference sample and the intra prediction mode, Prediction samples can be obtained. In this case, when the intra prediction mode is a planner mode, the prediction sample is a first prediction sample using at least one reference sample placed on the same horizontal line as the prediction target sample and at least one placed on the same vertical line as the prediction target sample. It may be generated based on the second prediction sample using the reference sample of.

The video signal encoding method and apparatus according to the present invention derive a reference sample for a current block, determine an intra prediction mode of the current block, and use the reference sample and the intra prediction mode, Prediction samples can be obtained. In this case, when the intra prediction mode is a planner mode, the prediction sample is a first prediction sample using at least one reference sample placed on the same horizontal line as the prediction target sample and at least one placed on the same vertical line as the prediction target sample. It may be generated based on the second prediction sample using the reference sample of.

In the video signal encoding / decoding method and apparatus according to the present invention, the reference sample includes a top reference sample and a left reference sample adjacent to the current block, and the first prediction sample is the left reference sample and the top reference sample. Generated using at least one of a right reference sample derived based on a reference sample, and the second prediction sample is generated using at least one of a lower reference sample derived based on the top reference sample and the left reference sample Can be.

In the video signal encoding / decoding method and apparatus according to the present invention, the position of the upper reference sample used to derive the right reference sample, or the position of the left reference sample used to derive the lower reference sample is It may be variably determined according to the size or shape of the current block.

In the video signal encoding / decoding method and apparatus according to the present invention, the first prediction sample is generated based on a weighted sum between the left reference sample and the right reference sample, and the second prediction sample is referred to the upper reference. A weighted sum between a sample and the bottom reference sample may be generated.

In the video signal encoding / decoding method and apparatus according to the present invention, the number of reference samples used to derive the first prediction sample or the second prediction sample may be differently determined according to the position of the prediction target sample.

In the video signal encoding / decoding method and apparatus according to the present invention, the prediction sample may be generated based on a weighted sum of the first prediction sample and the second prediction sample.

In the video signal encoding / decoding method and apparatus according to the present invention, weights for the first prediction sample and the second prediction sample may be differently determined according to the shape of the current block.

The features briefly summarized above with respect to the present invention are merely exemplary aspects of the detailed description of the invention that follows, and do not limit the scope of the invention.

According to the present invention, intra prediction can be efficiently performed on an encoding / decoding target block.

According to the present invention, the prediction efficiency can be improved by deriving a new reference sample based on previously derived reference samples under planner mode.

According to the present invention, the prediction efficiency can be improved by deriving a prediction sample based on the weighted sum of the plurality of reference samples.

The effects obtainable in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

1 is a block diagram illustrating an image encoding apparatus according to an embodiment of the present invention.

2 is a block diagram illustrating an image decoding apparatus according to an embodiment of the present invention.

FIG. 3 illustrates an example in which a coding block is hierarchically divided based on a tree structure according to an embodiment to which the present invention is applied.

4 is a diagram illustrating a partition type in which binary tree based partitioning is allowed as an embodiment to which the present invention is applied.

FIG. 5 is a diagram illustrating an example in which only a specific type of binary tree based partitioning is allowed as an embodiment to which the present invention is applied.

FIG. 6 is a diagram for explaining an example in which information related to a binary tree split permission number is encoded / decoded according to an embodiment to which the present invention is applied.

7 is a diagram illustrating a partition mode that can be applied to a coding block as an embodiment to which the present invention is applied.

8 illustrates a type of intra prediction mode that is pre-defined in an image encoder / decoder as an embodiment to which the present invention is applied.

9 illustrates a type of extended intra prediction mode according to an embodiment to which the present invention is applied.

10 is a flowchart schematically illustrating an intra prediction method according to an embodiment to which the present invention is applied.

FIG. 11 illustrates a method of correcting a prediction sample of a current block based on difference information of neighboring samples according to an embodiment to which the present invention is applied.

12 and 13 illustrate a method of correcting a prediction sample based on a predetermined correction filter according to an embodiment to which the present invention is applied.

14 illustrates a range of a reference sample for intra prediction as an embodiment to which the present invention is applied.

15 to 17 illustrate an example of reference sample filtering as an embodiment to which the present invention is applied.

18 illustrates an example of deriving a right reference sample or a lower reference sample using a plurality of reference samples according to an embodiment of the present invention.

19 and 20 are diagrams for explaining determining a right reference sample and a lower reference sample for a non-square block according to an embodiment of the present invention.

21 is a flowchart illustrating a process of obtaining a residual sample as an embodiment to which the present invention is applied.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

Referring to FIG. 1, the image encoding apparatus 100 may include a picture splitter 110, a

predictor

120 and 125, a transformer 130, a quantizer 135, a realigner 160, and an entropy encoder. 165, an inverse quantizer 140, an inverse transformer 145, a filter 150, and a memory 155.

Each of the components shown in FIG. 1 is independently illustrated to represent different characteristic functions in the image encoding apparatus, and does not mean that each of the components is made of separate hardware or one software component unit. In other words, each component is included in each component for convenience of description, and at least two of the components may be combined into one component, or one component may be divided into a plurality of components to perform a function. Integrated and separate embodiments of the components are also included within the scope of the present invention without departing from the spirit of the invention.

In addition, some of the components may not be essential components for performing essential functions in the present invention, but may be optional components for improving performance. The present invention can be implemented including only the components essential for implementing the essentials of the present invention except for the components used for improving performance, and the structure including only the essential components except for the optional components used for improving performance. Also included in the scope of the present invention.

The picture dividing unit 110 may divide the input picture into at least one processing unit. In this case, the processing unit may be a prediction unit (PU), a transform unit (TU), or a coding unit (CU). The picture dividing unit 110 divides one picture into a combination of a plurality of coding units, prediction units, and transformation units, and combines one coding unit, prediction unit, and transformation unit on a predetermined basis (eg, a cost function). You can select to encode the picture.

For example, one picture may be divided into a plurality of coding units. In order to split a coding unit in a picture, a recursive tree structure such as a quad tree structure may be used, and coding is divided into other coding units by using one image or a largest coding unit as a root. The unit may be split with as many child nodes as the number of split coding units. Coding units that are no longer split according to certain restrictions become leaf nodes. That is, when it is assumed that only square division is possible for one coding unit, one coding unit may be split into at most four other coding units.

Hereinafter, in an embodiment of the present invention, a coding unit may be used as a unit for encoding or may be used as a unit for decoding.

The prediction unit may be split in the form of at least one square or rectangle having the same size in one coding unit, or the prediction unit of any one of the prediction units split in one coding unit is different from one another. It may be divided to have a different shape and / or size than the unit.

When generating the prediction unit that performs the intra prediction based on the coding unit, when the prediction unit is not the minimum coding unit, the intra prediction may be performed without splitting into a plurality of prediction units NxN.

The

predictors

120 and 125 may include an inter predictor 120 that performs inter prediction and an intra predictor 125 that performs intra prediction. Whether to use inter prediction or intra prediction on the prediction unit may be determined, and specific information (eg, an intra prediction mode, a motion vector, a reference picture, etc.) according to each prediction method may be determined. In this case, the processing unit in which the prediction is performed may differ from the processing unit in which the prediction method and the details are determined. For example, the method of prediction and the prediction mode may be determined in the prediction unit, and the prediction may be performed in the transform unit. The residual value (residual block) between the generated prediction block and the original block may be input to the transformer 130. In addition, prediction mode information and motion vector information used for prediction may be encoded by the entropy encoder 165 together with the residual value and transmitted to the decoder. When a specific encoding mode is used, the original block may be encoded as it is and transmitted to the decoder without generating the prediction block through the

prediction units

120 and 125.

The inter prediction unit 120 may predict the prediction unit based on the information of at least one of the previous picture or the next picture of the current picture. In some cases, the inter prediction unit 120 may predict the prediction unit based on the information of the partial region in which the encoding is completed in the current picture. You can also predict units. The inter predictor 120 may include a reference picture interpolator, a motion predictor, and a motion compensator.

The reference picture interpolator may receive reference picture information from the memory 155 and generate pixel information of an integer pixel or less in the reference picture. In the case of luminance pixels, a DCT based 8-tap interpolation filter having different filter coefficients may be used to generate pixel information of integer pixels or less in units of 1/4 pixels. In the case of a chrominance signal, a DCT-based interpolation filter having different filter coefficients may be used to generate pixel information of an integer pixel or less in units of 1/8 pixels.

The motion predictor may perform motion prediction based on the reference picture interpolated by the reference picture interpolator. As a method for calculating a motion vector, various methods such as full search-based block matching algorithm (FBMA), three step search (TSS), and new three-step search algorithm (NTS) may be used. The motion vector may have a motion vector value of 1/2 or 1/4 pixel units based on the interpolated pixels. The motion prediction unit may predict the current prediction unit by using a different motion prediction method. As the motion prediction method, various methods such as a skip method, a merge method, an advanced motion vector prediction (AMVP) method, an intra block copy method, and the like may be used.

The intra predictor 125 may generate a prediction unit based on reference pixel information around the current block, which is pixel information in the current picture. If the neighboring block of the current prediction unit is a block that has performed inter prediction, and the reference pixel is a pixel that has performed inter prediction, the reference pixel of the block that has performed intra prediction around the reference pixel included in the block where the inter prediction has been performed Can be used as a substitute for information. That is, when the reference pixel is not available, the unavailable reference pixel information may be replaced with at least one reference pixel among the available reference pixels.

In intra prediction, a prediction mode may have a directional prediction mode using reference pixel information according to a prediction direction, and a non-directional mode using no directional information when performing prediction. The mode for predicting the luminance information and the mode for predicting the color difference information may be different, and the intra prediction mode information or the predicted luminance signal information used for predicting the luminance information may be utilized to predict the color difference information.

When performing intra prediction, if the size of the prediction unit and the size of the transform unit are the same, the intra prediction on the prediction unit is performed based on the pixels on the left of the prediction unit, the pixels on the upper left, and the pixels on the top. Can be performed. However, when performing intra prediction, if the size of the prediction unit is different from that of the transform unit, intra prediction may be performed using a reference pixel based on the transform unit. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The intra prediction method may generate a prediction block after applying an adaptive intra smoothing (AIS) filter to a reference pixel according to a prediction mode. The type of AIS filter applied to the reference pixel may be different. In order to perform the intra prediction method, the intra prediction mode of the current prediction unit may be predicted from the intra prediction mode of the prediction unit existing around the current prediction unit. When the prediction mode of the current prediction unit is predicted by using the mode information predicted from the neighboring prediction unit, if the intra prediction mode of the current prediction unit and the neighboring prediction unit is the same, the current prediction unit and the neighboring prediction unit using the predetermined flag information If the prediction modes of the current prediction unit and the neighboring prediction unit are different, entropy encoding may be performed to encode the prediction mode information of the current block.

Also, a residual block may include a prediction unit performing prediction based on the prediction units generated by the

prediction units

120 and 125 and residual information including residual information that is a difference from an original block of the prediction unit. The generated residual block may be input to the transformer 130.

The transform unit 130 converts the residual block including residual information of the original block and the prediction unit generated by the

prediction units

120 and 125 into a discrete cosine transform (DCT), a discrete sine transform (DST), and a KLT. You can convert using the same conversion method. Whether to apply DCT, DST, or KLT to transform the residual block may be determined based on intra prediction mode information of the prediction unit used to generate the residual block.

The quantization unit 135 may quantize the values converted by the transformer 130 into the frequency domain. The quantization coefficient may change depending on the block or the importance of the image. The value calculated by the quantization unit 135 may be provided to the inverse quantization unit 140 and the reordering unit 160.

The reordering unit 160 may reorder coefficient values with respect to the quantized residual value.

The reordering unit 160 may change the two-dimensional block shape coefficients into a one-dimensional vector form through a coefficient scanning method. For example, the reordering unit 160 may scan from DC coefficients to coefficients in the high frequency region by using a Zig-Zag scan method and change them into one-dimensional vectors. Depending on the size of the transform unit and the intra prediction mode, a vertical scan that scans two-dimensional block shape coefficients in a column direction instead of a zig-zag scan may be used, and a horizontal scan that scans two-dimensional block shape coefficients in a row direction. That is, according to the size of the transform unit and the intra prediction mode, it is possible to determine which scan method among the zig-zag scan, the vertical scan, and the horizontal scan is used.

The entropy encoder 165 may perform entropy encoding based on the values calculated by the reordering unit 160. Entropy encoding may use various encoding methods such as, for example, Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The entropy encoder 165 receives residual value coefficient information, block type information, prediction mode information, partition unit information, prediction unit information, transmission unit information, and motion of the coding unit from the reordering unit 160 and the

prediction units

120 and 125. Various information such as vector information, reference frame information, interpolation information of a block, and filtering information can be encoded.

The entropy encoder 165 may entropy encode a coefficient value of a coding unit input from the reordering unit 160.

The inverse quantizer 140 and the inverse transformer 145 inverse quantize the quantized values in the quantizer 135 and inversely transform the transformed values in the transformer 130. The residual value generated by the inverse quantizer 140 and the inverse transformer 145 is reconstructed by combining the prediction units predicted by the motion estimator, the motion compensator, and the intra predictor included in the

predictors

120 and 125. You can create a Reconstructed Block.

The filter unit 150 may include at least one of a deblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion caused by boundaries between blocks in the reconstructed picture. In order to determine whether to perform deblocking, it may be determined whether to apply a deblocking filter to the current block based on the pixels included in several columns or rows included in the block. When the deblocking filter is applied to the block, a strong filter or a weak filter may be applied according to the required deblocking filtering strength. In addition, in applying the deblocking filter, horizontal filtering and vertical filtering may be performed in parallel when vertical filtering and horizontal filtering are performed.

The offset correction unit may correct the offset with respect to the original image on a pixel-by-pixel basis for the deblocking image. In order to perform offset correction for a specific picture, the pixels included in the image are divided into a predetermined number of areas, and then, an area to be offset is determined, an offset is applied to the corresponding area, or offset considering the edge information of each pixel. You can use this method.

Adaptive Loop Filtering (ALF) may be performed based on a value obtained by comparing the filtered reconstructed image with the original image. After dividing the pixels included in the image into a predetermined group, one filter to be applied to the group may be determined and filtering may be performed for each group. For information related to whether to apply ALF, a luminance signal may be transmitted for each coding unit (CU), and the shape and filter coefficient of an ALF filter to be applied may vary according to each block. In addition, regardless of the characteristics of the block to be applied, the same type (fixed form) of the ALF filter may be applied.

The memory 155 may store the reconstructed block or picture calculated by the filter unit 150, and the stored reconstructed block or picture may be provided to the

predictors

120 and 125 when performing inter prediction.

Referring to FIG. 2, the image decoder 200 includes an entropy decoder 210, a reordering unit 215, an inverse quantizer 220, an inverse transformer 225, a

predictor

230, 235, and a filter unit ( 240, a memory 245 may be included.

When an image bitstream is input from the image encoder, the input bitstream may be decoded by a procedure opposite to that of the image encoder.

The entropy decoder 210 may perform entropy decoding in a procedure opposite to that of the entropy encoding performed by the entropy encoder of the image encoder. For example, various methods such as Exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC) may be applied to the method performed by the image encoder.

The entropy decoder 210 may decode information related to intra prediction and inter prediction performed by the encoder.

The reordering unit 215 may reorder the entropy decoded bitstream by the entropy decoding unit 210 based on a method of rearranging the bitstream. Coefficients expressed in the form of a one-dimensional vector may be reconstructed by reconstructing the coefficients in a two-dimensional block form. The reordering unit 215 may be realigned by receiving information related to coefficient scanning performed by the encoder and performing reverse scanning based on the scanning order performed by the corresponding encoder.

The inverse quantization unit 220 may perform inverse quantization based on the quantization parameter provided by the encoder and the coefficient values of the rearranged block.

The inverse transform unit 225 may perform an inverse transform, i.e., an inverse DCT, an inverse DST, and an inverse KLT, for a quantization result performed by the image encoder, that is, a DCT, DST, and KLT. Inverse transformation may be performed based on a transmission unit determined by the image encoder. The inverse transform unit 225 of the image decoder may selectively perform a transform scheme (eg, DCT, DST, KLT) according to a plurality of pieces of information such as a prediction method, a size of a current block, and a prediction direction.

The

prediction units

230 and 235 may generate the prediction block based on the prediction block generation related information provided by the entropy decoder 210 and previously decoded blocks or picture information provided by the memory 245.

As described above, when performing the intra prediction in the same manner as the operation in the image encoder, when the size of the prediction unit and the size of the transformation unit are the same, the pixel present on the left side, the pixel present on the upper left side, and the upper part exist Intra prediction is performed on a prediction unit based on a pixel, but when intra prediction is performed, when the size of the prediction unit and the size of the transformation unit are different, intra prediction may be performed using a reference pixel based on the transformation unit. Can be. In addition, intra prediction using NxN division may be used only for a minimum coding unit.

The

predictors

230 and 235 may include a prediction unit determiner, an inter predictor, and an intra predictor. The prediction unit determiner receives various information such as prediction unit information input from the entropy decoder 210, prediction mode information of the intra prediction method, and motion prediction related information of the inter prediction method, and distinguishes the prediction unit from the current coding unit, and predicts It may be determined whether the unit performs inter prediction or intra prediction. The inter prediction unit 230 predicts the current prediction based on information included in at least one of a previous picture or a subsequent picture of the current picture including the current prediction unit by using information required for inter prediction of the current prediction unit provided by the image encoder. Inter prediction may be performed on a unit. Alternatively, inter prediction may be performed based on information of some regions pre-restored in the current picture including the current prediction unit.

In order to perform inter prediction, a motion prediction method of a prediction unit included in a coding unit based on a coding unit includes a skip mode, a merge mode, an AMVP mode, and an intra block copy mode. It can be determined whether or not it is a method.

The intra predictor 235 may generate a prediction block based on pixel information in the current picture. When the prediction unit is a prediction unit that has performed intra prediction, intra prediction may be performed based on intra prediction mode information of the prediction unit provided by the image encoder. The intra predictor 235 may include an adaptive intra smoothing (AIS) filter, a reference pixel interpolator, and a DC filter. The AIS filter is a part of filtering the reference pixel of the current block and determines whether to apply the filter according to the prediction mode of the current prediction unit. AIS filtering may be performed on the reference pixel of the current block by using the prediction mode and the AIS filter information of the prediction unit provided by the image encoder. If the prediction mode of the current block is a mode that does not perform AIS filtering, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unit that performs intra prediction based on a pixel value interpolating the reference pixel, the reference pixel interpolator may generate a reference pixel having an integer value or less by interpolating the reference pixel. If the prediction mode of the current prediction unit is a prediction mode for generating a prediction block without interpolating the reference pixel, the reference pixel may not be interpolated. The DC filter may generate the prediction block through filtering when the prediction mode of the current block is the DC mode.

The reconstructed block or picture may be provided to the filter unit 240. The filter unit 240 may include a deblocking filter, an offset correction unit, and an ALF.

Information about whether a deblocking filter is applied to a corresponding block or picture, and when the deblocking filter is applied to the corresponding block or picture, may be provided with information about whether a strong filter or a weak filter is applied. In the deblocking filter of the image decoder, the deblocking filter related information provided by the image encoder may be provided and the deblocking filtering of the corresponding block may be performed in the image decoder.

The offset correction unit may perform offset correction on the reconstructed image based on the type of offset correction and offset value information applied to the image during encoding.

The ALF may be applied to a coding unit based on ALF application information, ALF coefficient information, and the like provided from the encoder. Such ALF information may be provided included in a specific parameter set.

The memory 245 may store the reconstructed picture or block to use as a reference picture or reference block, and may provide the reconstructed picture to the output unit.

As described above, in the embodiment of the present invention, a coding unit is used as a coding unit for convenience of description, but may also be a unit for performing decoding as well as encoding.

In addition, the current block represents a block to be encoded / decoded, and according to the encoding / decoding step, a coding tree block (or a coding tree unit), an encoding block (or a coding unit), a transform block (or a transform unit), or a prediction block. (Or prediction unit) or the like.

One picture may be divided into square or non-square basic blocks and encoded / decoded. In this case, the basic block may be referred to as a coding tree unit. A coding tree unit may be defined as a coding unit of the largest size allowed in a sequence or slice. Information regarding whether the coding tree unit is square or non-square or the size of the coding tree unit may be signaled through a sequence parameter set, a picture parameter set or a slice header. The coding tree unit may be divided into smaller sized partitions. In this case, when the partition generated by dividing the coding tree unit is called depth 1, the partition generated by dividing the partition having depth 1 may be defined as depth 2. That is, a partition generated by dividing a partition that is a depth k in a coding tree unit may be defined as having a depth k + 1.

A partition of any size generated as the coding tree unit is split may be defined as a coding unit. The coding unit may be split recursively or split into basic units for performing prediction, quantization, transform, or in-loop filtering. For example, an arbitrary size partition generated as a coding unit is divided may be defined as a coding unit or a transform unit or a prediction unit that is a basic unit for performing prediction, quantization, transform, or in-loop filtering.

Partitioning of the coding tree unit or the coding unit may be performed based on at least one of a vertical line or a horizontal line. In addition, the number of vertical lines or horizontal lines partitioning the coding tree unit or the coding unit may be at least one. For example, by splitting a coding tree unit or coding unit into two partitions using one vertical line or one horizontal line, or by using two vertical lines or two horizontal lines, the coding tree unit or coding unit into three partitions. Can be divided Alternatively, one vertical line and one horizontal line may be used to divide a coding tree unit or coding unit into four partitions of 1/2 length and width.

When the coding tree unit or the coding unit is divided into a plurality of partitions using at least one vertical line or at least one horizontal line, the partitions may have a uniform size or may have different sizes. Alternatively, one partition may have a different size than the other partition.

In the embodiments described below, it is assumed that a coding tree unit or a coding unit is divided into a quad tree or binary tree structure. However, splitting of a coding tree unit or coding units using more vertical lines or more horizontal lines is also possible.

The input video signal is decoded in predetermined block units, and the basic unit for decoding the input video signal in this way is called a coding block. The coding block may be a unit for performing intra / inter prediction, transformation, and quantization. In addition, a prediction mode (eg, an intra prediction mode or an inter prediction mode) is determined on a coding block basis, and prediction blocks included in the coding block may share the determined prediction mode. The coding block can be a square or non-square block with any size in the range 8x8 to 64x64, and can be a square or non-square block with a size of 128x128, 256x256 or more.

In detail, the coding block may be hierarchically divided based on at least one of a quad tree and a binary tree. Here, quad tree-based partitioning may mean a method in which a 2Nx2N coding block is divided into four NxN coding blocks, and binary tree-based partitioning may mean a method in which one coding block is divided into two coding blocks. Even if binary tree-based partitioning is performed, there may be a square coding block at a lower depth.

Binary tree-based partitioning may be performed symmetrically or asymmetrically. The coding block divided based on the binary tree may be a square block or a non-square block such as a rectangle. For example, a partition type that allows binary tree based partitioning may be symmetric 2NxN (horizontal non-square coding unit) or Nx2N (vertical non-square coding unit), asymmetric, as in the example shown in FIG. It may include at least one of asymmetric nLx2N, nRx2N, 2NxnU or 2NxnD.

Binary tree-based partitioning may be limitedly limited to either symmetric or asymmetric partitions. In this case, configuring the coding tree unit into square blocks may correspond to quad tree CU partitioning, and configuring the coding tree unit into symmetric non-square blocks may correspond to binary tree partitioning. Configuring the coding tree unit into square blocks and symmetric non-square blocks may correspond to quad and binary tree CU partitioning.

Binary tree-based partitioning may be performed on coding blocks in which quadtree-based partitioning is no longer performed. Quad tree-based partitioning may no longer be performed on a coding block partitioned based on a binary tree.

In addition, the division of the lower depth may be determined depending on the division type of the upper depth. For example, when binary tree-based partitioning is allowed in two or more depths, only a binary tree-based partitioning of the same type as a binary tree partitioning of an upper depth may be allowed in a lower depth. For example, when the binary tree based splitting is performed in the 2NxN form at the upper depth, the binary tree based splitting in the 2NxN form may be performed at the lower depth. Alternatively, when binary tree-based partitioning is performed in an Nx2N form at an upper depth, Nx2N-type binary tree-based partitioning may be allowed in a lower depth.

Conversely, it is also possible to allow only binary tree-based partitioning of a form different from the binary tree splitting form of the upper depth in the lower depth.

For sequences, slices, coding tree units, or coding units, only certain types of binary tree based partitioning may be used. For example, the 2NxN or Nx2N type binary tree based partitioning may be limited to the coding tree unit. The allowed partition type may be predefined in the encoder or the decoder, and information about the allowed partition type or the not allowed partition type may be encoded and signaled through a bitstream.

5 illustrates an example in which only a specific type of binary tree based partitioning is allowed. FIG. 5A illustrates an example in which only binary tree-based partitioning in the form of Nx2N is allowed, and FIG. 5B illustrates an example in which only binary tree-based partitioning in the form of 2NxN is allowed. Information indicating a quad tree based partition, information about a size / depth of a coding block allowing quad tree based partitioning, and binary tree based partitioning to implement the quad tree or binary tree based adaptive partitioning Information about the size / depth of coding blocks that allow binary tree based splitting, information about the size / depth of coding blocks that do not allow binary tree based splitting, or whether the binary tree based splitting is vertical, or Information about whether the image is in the horizontal direction may be used.

In addition, for the coding tree unit or the predetermined coding unit, the number of times that binary tree splitting is allowed, the depth for which binary tree splitting is allowed or the number of depths for which binary tree splitting is allowed may be obtained. The information may be encoded in a coding tree unit or a coding unit and transmitted to a decoder through a bitstream.

For example, a syntax 'max_binary_depth_idx_minus1' indicating a maximum depth that allows binary tree splitting may be encoded / decoded through the bitstream through the bitstream. In this case, max_binary_depth_idx_minus1 + 1 may indicate the maximum depth allowed for binary tree splitting.

Referring to the example illustrated in FIG. 6, in FIG. 6, binary tree splitting is performed on a coding unit having a depth of 2 and a coding unit having a depth of 3. Accordingly, information indicating the number of times binary tree splitting has been performed in the coding tree unit (2 times), information indicating the maximum depth (depth 3) allowed for binary tree splitting in the coding tree unit, or binary tree splitting in the coding tree unit is obtained. At least one of information indicating the number of allowed depths (2, depth 2, and depth 3) may be encoded / decoded through the bitstream.

As another example, at least one of the number of times that the binary tree split is allowed, the depth in which the binary tree split is allowed, or the number of the depths in which the binary tree split is allowed may be obtained for each sequence and slice. For example, the information may be encoded in a sequence, picture or slice unit and transmitted through a bitstream. Accordingly, at least one of the number of binary tree splits, the maximum depth allowed for binary tree splits, or the number of depths allowed for binary tree splits may be different in the first and second slices. For example, in the first slice, binary tree splitting is allowed only at one depth, while in the second slice, binary tree splitting may be allowed at two depths.

As another example, at least one of the number of times that a binary tree split is allowed, the depth that allows a binary tree split, or the number of depths that allow a binary tree split may be differently set according to a temporal ID (TemporalID) of a slice or a picture. have. Here, the temporal level identifier TemporalID may be used to identify each of a plurality of layers of an image having at least one scalability among a view, a spatial, a temporal, or a quality. will be.

As illustrated in FIG. 3, the first coding block 300 having a split depth of k may be divided into a plurality of second coding blocks based on a quad tree. For example, the second coding blocks 310 to 340 are square blocks having half the width and the height of the first coding block, and the split depth of the second coding block may be increased to k + 1.

The second coding block 310 having the division depth k + 1 may be divided into a plurality of third coding blocks having the division depth k + 2. Partitioning of the second coding block 310 may be selectively performed using either a quart tree or a binary tree according to a partitioning scheme. Here, the splitting scheme may be determined based on at least one of information indicating splitting based on the quad tree or information indicating splitting based on the binary tree.

When the second coding block 310 is divided on the basis of the quart tree, the second coding block 310 is divided into four third coding blocks 310a having half the width and the height of the second coding block, The split depth can be increased to k + 2. On the other hand, when the second coding block 310 is divided on a binary tree basis, the second coding block 310 may be split into two third coding blocks. In this case, each of the two third coding blocks is a non-square block having one half of the width and the height of the second coding block, and the split depth may be increased to k + 2. The second coding block may be determined as a non-square block in the horizontal direction or the vertical direction according to the division direction, and the division direction may be determined based on information about whether the binary tree-based division is the vertical direction or the horizontal direction.

Meanwhile, the second coding block 310 may be determined as an end coding block that is no longer split based on the quad tree or the binary tree, and in this case, the corresponding coding block may be used as a prediction block or a transform block.

The third coding block 310a may be determined as an end coding block like the division of the second coding block 310, or may be further divided based on a quad tree or a binary tree.

Meanwhile, the third coding block 310b split based on the binary tree may be further divided into a vertical coding block 310b-2 or a horizontal coding block 310b-3 based on the binary tree, and corresponding coding The partition depth of the block can be increased to k + 3. Alternatively, the third coding block 310b may be determined as an end coding block 310b-1 that is no longer split based on the binary tree, in which case the coding block 310b-1 may be used as a prediction block or a transform block. Can be. However, the above-described partitioning process allows information about the size / depth of a coding block that allows quad-tree based partitioning, information about the size / depth of the coding block that allows binary tree-based partitioning, or binary-tree based partitioning. It may be limitedly performed based on at least one of information about the size / depth of the coding block that is not.

The size of the coding block may be limited to a predetermined number, or the size of the coding block in the predetermined unit may have a fixed value. As an example, the size of the coding block in the sequence or the size of the coding block in the picture may be limited to 256x256, 128x128 or 32x32. Information representing the size of a coding block in a sequence or picture may be signaled through a sequence header or picture header.

As a result of the division based on the quad tree and the binary tree, the coding unit may take a square or a rectangle of any size.

The coding block is encoded using at least one of a skip mode, an intra prediction, an inter prediction, or a skip method. When the coding block is determined, a prediction block may be determined through prediction division of the coding block. Predictive partitioning of a coding block may be performed by a partition mode (Part_mode) indicating a partition type of a coding block. The size or shape of the prediction block may be determined according to the partition mode of the coding block. For example, the size of the prediction block determined according to the partition mode may have a value equal to or smaller than the size of the coding block.

FIG. 7 is a diagram illustrating a partition mode that may be applied to a coding block when the coding block is encoded by inter prediction.

When the coding block is encoded by inter prediction, any one of eight partition modes may be applied to the coding block, as shown in the example illustrated in FIG. 7.

When a coding block is encoded by intra prediction, partition mode PART_2Nx2N or PART_NxN may be applied to the coding block.

PART_NxN may be applied when the coding block has a minimum size. Here, the minimum size of the coding block may be predefined in the encoder and the decoder. Alternatively, information about the minimum size of the coding block may be signaled through the bitstream. As an example, the minimum size of the coding block is signaled through the slice header, and accordingly, the minimum size of the coding block may be defined for each slice.

In general, the size of the prediction block may have a size of 64x64 to 4x4. However, when the coding block is encoded by inter prediction, when the motion compensation is performed, the prediction block may not have a 4x4 size in order to reduce the memory bandwidth.

The image encoder / decoder may perform intra prediction using any one of pre-defined intra prediction modes. The pre-defined intra prediction mode for intra prediction may consist of a non-directional prediction mode (eg, planar mode, DC mode) and 33 directional prediction modes.

Alternatively, more directional prediction modes may be used than 33 directional prediction modes to increase the accuracy of intra prediction. That is, the angle of the directional prediction mode may be further subdivided to define M extended directional prediction modes (M> 33), and the predetermined angle may be defined using at least one of the 33 pre-defined directional prediction modes. It is also possible to derive and use a directional prediction mode with.

A larger number of intra prediction modes may be used than the 35 intra prediction modes shown in FIG. 8. For example, the angle of the directional prediction mode is further subdivided, or the directional prediction mode having a predetermined angle is decoded by using at least one of a predetermined number of directional modes, so that the number of the directional prediction modes is greater than 35 intra prediction modes. Intra prediction mode may be used. In this case, using an intra prediction mode larger than 35 intra prediction modes may be referred to as an extended intra prediction mode.

9 is an example of an extended intra prediction mode, and the extended intra prediction mode may be configured of two non-directional prediction modes and 65 extended directional prediction modes. The extended intra prediction mode may be used in the same way for the luminance component and the chrominance component, or may use a different number of intra prediction modes for each component. For example, 67 extended intra prediction modes may be used in the luminance component, and 35 intra prediction modes may be used in the chrominance component.

Alternatively, intra prediction may be performed using different numbers of intra prediction modes according to a color difference format. For example, in 4: 2: 0 format, intra prediction may be performed using 67 intra prediction modes in a luminance component, and 35 intra prediction modes may be used in a chrominance component, and in 4: 4: 4 format. Intra prediction may be used using 67 intra prediction modes in both a luminance component and a chrominance component.

Alternatively, intra prediction may be performed using different numbers of intra prediction modes according to the size and / or shape of the block. That is, intra prediction may be performed using 35 intra prediction modes or 67 intra prediction modes according to the size and / or shape of the PU or CU. For example, if the size of a CU or PU is less than 64x64 or an asymmetric partition, intra prediction can be performed using 35 intra prediction modes, and the size of the CU or PU is greater than or equal to 64x64. In this case, intra prediction may be performed using 67 intra prediction modes. Intra_2Nx2N may allow 65 directional intra prediction modes, and Intra_NxN may allow only 35 directional intra prediction modes.

The size of a block to which the extended intra prediction mode is applied may be set differently for each sequence, picture, or slice. For example, in the first slice, the extended intra prediction mode is set to be applied to a block larger than 64x64 (eg, a CU or a PU), and in the second slice, the extended intra prediction mode is set to be applied to a block larger than 32x32. Can be. Information representing the size of a block to which the extended intra prediction mode is applied may be signaled for each sequence, picture, or slice unit. For example, the information indicating the size of a block to which the extended intra prediction mode is applied may be defined as 'log2_extended_intra_mode_size_minus4' after taking a log value to the size of the block and subtracting an integer 4. For example, a value of 0 for log2_extended_intra_mode_size_minus4 indicates that an extended intra prediction mode may be applied to a block having a size larger than 16x16 or a block larger than 16x16. It may indicate that the extended intra prediction mode may be applied to a block having a block size or a block having a size larger than 32 × 32.

As described above, the number of intra prediction modes may be determined in consideration of at least one of a color difference component, a color difference format, a size, or a shape of a block. The intra prediction mode candidates (for example, the number of MPMs) used to determine the intra prediction mode of the block to be encoded / decoded are not limited to the examples described above. It may be determined accordingly. A method of determining an intra prediction mode of an encoding / decoding target block and a method of performing intra prediction using the determined intra prediction mode will be described with reference to the drawings to be described later.

Referring to FIG. 10, an intra prediction mode of a current block may be determined (S1000).

In detail, the intra prediction mode of the current block may be derived based on the candidate list and the index. Here, the candidate list includes a plurality of candidates, and the plurality of candidates may be determined based on the intra prediction mode of the neighboring block adjacent to the current block. The neighboring block may include at least one of blocks located at the top, bottom, left, right, or corner of the current block. The index may specify any one of a plurality of candidates belonging to the candidate list. The candidate specified by the index may be set to the intra prediction mode of the current block.

The intra prediction mode used by the neighboring block for intra prediction may be set as a candidate. In addition, an intra prediction mode having a direction similar to that of the neighboring block may be set as a candidate. Here, the intra prediction mode having similar directionality may be determined by adding or subtracting a predetermined constant value to the intra prediction mode of the neighboring block. The predetermined constant value may be an integer of 1, 2 or more.

The candidate list may further include a default mode. The default mode may include at least one of a planner mode, a DC mode, a vertical mode, and a horizontal mode. The default mode may be adaptively added in consideration of the maximum number of candidates included in the candidate list of the current block.

The maximum number of candidates that can be included in the candidate list may be three, four, five, six, or more. The maximum number of candidates that may be included in the candidate list may be a fixed value preset in the image encoder / decoder and may be variably determined based on the attributes of the current block. The attribute may mean the position / size / type of the block, the number / type of intra prediction modes that the block can use, the color difference attribute, the color difference format, and the like. Alternatively, information indicating the maximum number of candidates included in the candidate list may be separately signaled, and the maximum number of candidates included in the candidate list may be variably determined using the information. Information indicating the maximum number of candidates may be signaled at least one of a sequence level, a picture level, a slice level, or a block level.

When the extended intra prediction mode and the 35 pre-defined intra prediction modes are selectively used, the intra prediction mode of the neighboring block is converted into an index corresponding to the extended intra prediction mode, or corresponding to the 35 intra prediction modes. The candidate can be derived by converting to an index. A pre-defined table may be used for the conversion of the index, or a scaling operation based on a predetermined value may be used. Here, the pre-defined table may define a mapping relationship between different groups of intra prediction modes (eg, extended intra prediction modes and 35 intra prediction modes).

For example, if the left neighbor block uses 35 intra prediction modes and the intra prediction mode of the left neighbor block is 10 (horizontal mode), it is converted from the extended intra prediction mode to index 16 corresponding to the horizontal mode. Can be.

Alternatively, when the upper neighboring block uses the extended intra prediction mode and the intra prediction mode index of the upper neighboring block is 50 (vertical mode), it may be converted from the 35 intra prediction modes to the index 26 corresponding to the vertical mode. have.

Based on the above-described intra prediction mode determination method, an intra prediction mode may be derived independently of each of the luminance component and the chrominance component, and the chrominance component may be derived as a dependency on the intra prediction mode of the luminance component.

In detail, the intra prediction mode of the chrominance component may be determined based on the intra prediction mode of the luminance component, as shown in Table 1 below.

Intra_chroma_pred_mode[xCb][yCb] Intra_chroma_pred_mode [xCb] [yCb]	IntraPredModeY[xCb][yCb]IntraPredModeY [xCb] [yCb]
	00	2626	1010	1One	X(0<=X<=34)X (0 <= X <= 34)
00	3434	00	00	00	00
1One	2626	3434	2626	2626	2626
22	1010	1010	3434	1010	1010
33	1One	1One	1One	3434	1One
44	00	2626	1010	1One	XX

In Table 1, intra_chroma_pred_mode means information signaled to specify an intra prediction mode of a chrominance component, and IntraPredModeY represents an intra prediction mode of a luminance component.

Referring to FIG. 10, a reference sample for intra prediction of a current block may be derived (S1010).

In detail, a reference sample for intra prediction may be derived based on a neighboring sample of the current block. The peripheral sample may mean a reconstruction sample of the above-described peripheral block, which may be a reconstruction sample before the in-loop filter is applied or a reconstruction sample after the in-loop filter is applied.

The surrounding sample reconstructed before the current block may be used as the reference sample, and the surrounding sample filtered based on a predetermined intra filter may be used as the reference sample. Filtering the surrounding samples using an intra filter may be referred to as reference sample smoothing. The intra filter may include at least one of a first intra filter applied to a plurality of peripheral samples located on the same horizontal line or a second intra filter applied to a plurality of peripheral samples located on the same vertical line. Depending on the position of the peripheral sample, either the first intra filter or the second intra filter may be selectively applied, or two intra filters may be applied in duplicate. In this case, at least one filter coefficient of the first intra filter or the second intra filter may be (1, 2, 1), but is not limited thereto.

The filtering may be adaptively performed based on at least one of the intra prediction mode of the current block or the size of the transform block for the current block. For example, filtering may not be performed when the intra prediction mode of the current block is a DC mode, a vertical mode, or a horizontal mode. When the size of the transform block is NxM, filtering may not be performed. Here, N and M may be the same or different values, and may be any one of 4, 8, 16, or more values. As an example, when the size of the transform block is 4x4, filtering may not be performed. Alternatively, filtering may be selectively performed based on a comparison result between a difference between the intra prediction mode and the vertical mode (or the horizontal mode) of the current block and a pre-defined threshold. For example, filtering may be performed only when the difference between the intra prediction mode and the vertical mode of the current block is larger than the threshold. The threshold may be defined for each transform block size as shown in Table 2.

	8x8 transform 8x8 transform	16x16 transform16x16 transform	32x32 transform32x32 transform
Threshold Throshold	77	1One	00

The intra filter may be determined as one of a plurality of intra filter candidates pre-defined in the image encoder / decoder. To this end, a separate index for specifying an intra filter of the current block among the plurality of intra filter candidates may be signaled. Alternatively, the intra filter may be determined based on at least one of the size / shape of the current block, the size / shape of the transform block, the information about the filter strength, or the variation of surrounding samples.

Referring to FIG. 10, intra prediction may be performed using an intra prediction mode and a reference sample of a current block (S1020).

That is, the prediction sample of the current block may be obtained using the intra prediction mode determined in S1000 and the reference sample derived in S1010. However, in the case of intra prediction, since the boundary samples of the neighboring blocks are used, the quality of the predicted image may be degraded. Accordingly, the process may further include a correction process for the prediction sample generated through the above-described prediction process, which will be described in detail with reference to FIGS. 11 to 13. However, the correction process to be described later is not limited to being applied only to the intra prediction sample, but may also be applied to the inter prediction sample or the reconstruction sample.

The prediction sample of the current block may be corrected based on difference information of a plurality of neighboring samples for the current block. The correction may be performed on all prediction samples belonging to the current block, or may be performed only on prediction samples belonging to a predetermined partial region. Some areas may be one row / column or a plurality of rows / columns, which may be pre-configured areas for correction in the image encoder / decoder. For example, correction may be performed on one row / column positioned at the boundary of the current block or a plurality of rows / columns from the boundary of the current block. Alternatively, some regions may be variably determined based on at least one of the size / shape of the current block or the intra prediction mode.

The neighboring samples may belong to at least one of the neighboring blocks located at the top, left, and top left corners of the current block. The number of peripheral samples used for the calibration may be two, three, four or more. The position of the neighboring samples may be variably determined according to the position of the prediction sample to be corrected in the current block. Alternatively, some of the surrounding samples may have a fixed position regardless of the position of the prediction sample to be corrected, and others may have a variable position according to the position of the prediction sample to be corrected.

The difference information of the neighboring samples may mean a difference sample between the neighboring samples, or may mean a value obtained by scaling the difference sample to a predetermined constant value (eg, 1, 2, 3, etc.). Here, the predetermined constant value may be determined in consideration of the position of the prediction sample to be corrected, the position of the column or row to which the prediction sample to be corrected belongs, and the position of the prediction sample within the column or row.

For example, when the intra prediction mode of the current block is the vertical mode, the difference sample between the peripheral sample p (-1, y) adjacent to the left boundary of the current block and the upper left peripheral sample p (-1, -1) is used. As shown in Equation 1 below, a final prediction sample may be obtained.

For example, when the intra prediction mode of the current block is the horizontal mode, the difference sample between the neighboring sample p (x, -1) and the upper left neighboring sample p (-1, -1) adjacent to the upper boundary of the current block is used. As shown in Equation 2 below, a final prediction sample may be obtained.

For example, when the intra prediction mode of the current block is the vertical mode, the difference sample between the peripheral sample p (-1, y) adjacent to the left boundary of the current block and the upper left peripheral sample p (-1, -1) is used. The final prediction sample can be obtained. In this case, the difference sample may be added to the prediction sample, and the difference sample may be scaled to a predetermined constant value and then added to the prediction sample. The predetermined constant value used for scaling may be determined differently depending on the column and / or the row. For example, the prediction sample may be corrected as in

Equations

3 and 4 below.

For example, when the intra prediction mode of the current block is the horizontal mode, the difference sample between the neighboring sample p (x, -1) and the upper left neighboring sample p (-1, -1) adjacent to the upper boundary of the current block is used. The final prediction sample can be obtained, as described above in the vertical mode. For example, the prediction sample may be corrected as in

Equations

5 and 6 below.

The prediction sample may be corrected based on the surrounding sample of the prediction sample to be corrected and a predetermined correction filter. In this case, the neighboring sample may be specified by an angular line of the directional prediction mode of the current block, and may be one or more samples located on the same angular line as the prediction sample to be corrected. In addition, the neighboring sample may be a prediction sample belonging to the current block or may be a reconstruction sample belonging to a neighboring block reconstructed before the current block.

The number of taps, strength, or filter coefficients of the correction filter is at least one of the position of the prediction sample to be corrected, whether the prediction sample to be corrected is located at the boundary of the current block, the intra prediction mode of the current block, the angle of the directional prediction mode, the periphery It may be determined based on at least one of the prediction mode (inter or intra mode) of the block or the size / shape of the current block.

Referring to FIG. 12, when the index is 2 or 34 in the directional prediction mode, at least one prediction / restore sample located at the lower left of the prediction sample to be corrected as shown in FIG. Can be obtained. Here, the lower left prediction / restore sample may belong to the previous line of the line to which the prediction sample to be corrected belongs, which may belong to the same block as the current sample or may belong to a neighboring block adjacent to the current block.

Filtering on the prediction sample may be performed only on a line located at a block boundary or may be performed on a plurality of lines. A correction filter in which at least one of the filter tap number or the filter coefficient is different for each line may be used. For example, you can use the (1 / 2,1 / 2) filter for the left first line closest to the block boundary, the (12/16, 4/16) filter for the second line, and the third line. In the case of the (14/16, 2/16) filter, the fourth line may use the (15/16, 1/16) filter.

Alternatively, when the index in the directional prediction mode is a value between 3 and 6 or between 30 and 33, filtering may be performed at a block boundary as shown in FIG. 13, and the prediction sample may be corrected using a 3-tap correction filter. have. The filtering may be performed by using a 3-tap correction filter that receives the lower left sample of the predicted sample to be corrected, the lower sample of the lower left sample, and the predicted sample to be corrected. The position of the peripheral sample used in the correction filter may be determined differently based on the directional prediction mode. The filter coefficients of the correction filter may be determined differently according to the directional prediction mode.

Different correction filters may be applied depending on whether the neighboring block is an inter mode or an intra mode. When the neighboring block is encoded in the intra mode, a filtering method that adds more weight to the predictive sample may be used than when the neighboring block is encoded in the inter mode. For example, when the intra prediction mode is 34, the (1/2, 1/2) filter is used when the neighboring block is encoded in the inter mode, and (4/16) when the neighboring block is encoded in the intra mode. , 12/16) filters can be used.

The number of lines filtered in the current block may be different according to the size / shape of the current block (eg, coding block, prediction block). For example, if the size of the current block is less than or equal to 32x32, filter only one line at the block boundary; otherwise, filter on multiple lines, including one line at the block boundary. It may be.

12 and 13 will be described based on the case of using the 35 intra prediction modes mentioned in FIG. 7, but may be similarly / similarly applied to the case of using the extended intra prediction mode.

Intra prediction of the current block may be performed using a reference sample derived based on a reconstruction sample included in the neighboring block. Here, the reconstructed sample means that the encoding / decoding is completed before the encoding / decoding of the current block. For example, reference samples P (-1, -1), P (-1, y) (0 <= y <= 2N-1), P (x, -1) (0 <= x < = 2N-1), intra prediction may be performed on the current block. In this case, filtering may be selectively performed on the reference sample based on at least one of an intra prediction mode of the current block (eg, index, directionality, angle, etc. of the intra prediction mode) or a size of a transform block with respect to the current block. Can be.

In the encoder and the decoder, a reference sample may be filtered by using a predetermined intra filter. As an example, an intra filter having a filter coefficient of (1, 2, 1) or an intra filter having a coefficient of (2, 3, 6, 3, 2) may be used to derive a final reference sample to be used for intra prediction.

Alternatively, at least one of the plurality of intra filter candidates may be selected to perform filtering on the reference sample. Here, the plurality of intra filter candidates may differ from each other by at least one of filter intensity, filter coefficient, or tap number (eg, number of filter coefficients, filter length). The plurality of intra filter candidates may be defined in at least one of a sequence, a picture, a slice, and a block level. That is, a sequence, a picture, a slice, or a block to which the current block belongs may use the same plurality of intra filter candidates.

Hereinafter, for convenience of description, the plurality of intra filter candidates includes a first intra filter and a second intra filter, the first intra filter is a (1,2,1) 3-tap filter, and the second intra filter is Assume a (2,3,6,3,2) 5-tap filter.

When the reference sample is filtered by applying the first intra filter, the filtered reference sample may be derived as shown in Equation 7 below.

When the reference sample is filtered by applying the second intra filter, the filtered reference sample may be derived as in Equation 8 below.

In

Equations

7 and 8, x may be an integer between 0 and 2N-2, and y may be an integer between 0 and 2N-2.

Alternatively, any one of the plurality of intra filter candidates may be specified based on the position of the reference sample, and filtering may be performed on the reference sample using this. For example, a first intra filter may be applied to a reference sample belonging to a first range, and a second intra filter may be applied to a reference sample belonging to a second range. Here, the first range and the second range may be divided based on whether they are adjacent to a boundary of the current block, classified based on whether they are located at the top of the current block or on the left, or adjacent to a corner of the current block. It can be divided based on whether or not. For example, as shown in FIG. 15, reference samples P (-1, -1), P (-1,0), P (-1,1), ..., P (-) adjacent to the current block boundary 1, N-1) and P (0, -1), P (1, -1), ..., P (N-1, -1) by applying a first intra filter to filter as shown in Equation 7 In addition, the second intra filter may be applied to other reference samples that are not adjacent to the current block boundary, and may be filtered as shown in Equation 8. A plurality of intra filters based on the transform type used in the current block Any one of the candidates may be selected and used to perform filtering on the reference sample. Here, the transformation type may mean (1) a transformation scheme such as DCT, DST, or KLT, (2) a transformation mode indicator such as 2D transformation, 1D transformation, or no transformation, and (3) primary It can also mean the number of transformations, such as transformation and secondary transformation. Hereinafter, for convenience of explanation, it is assumed that the conversion type means a conversion scheme such as DCT, DST, and KLT.

For example, if the current block is encoded using DCT, filtering may be performed using a first intra filter. If the current block is encoded using DST, filtering may be performed using a second intra filter. have. Alternatively, if the current block is encoded using DCT or DST, filtering may be performed using the first intra filter, and if the current block is encoded using KLT, filtering may be performed using the second intra filter. have.

Filtering may be performed using a filter selected based on the above-described transform type of the current block and the position of the reference sample. For example, when encoded using the current block DCT, reference samples P (-1, -1), P (-1,0), P (-1,1), ..., P (-1, N-1) and P (0, -1), P (1, -1), ..., P (N-1, -1) perform filtering using the first intra filter, and other references. The sample may perform filtering using the second intra filter. If the current block is encoded using DST, reference samples P (-1, -1), P (-1,0), P (-1,1), ..., P (-1, N-1 ) P (0, -1), P (1, -1), ..., P (N-1, -1) perform filtering using the second intra filter, and other reference samples One intra filter may be used to perform filtering.

Any one of a plurality of intra filter candidates may be selected based on whether the transform type of the neighboring block including the reference sample is the same as the transform type of the current block, and filtering may be performed on the reference sample using the same. For example, if the current block and the neighboring block use the same transform type, filtering is performed using the first intra filter. If the current block and the neighboring block use different transform types, the second intra filter is used. Can be used to perform filtering.

Any one of a plurality of intra filter candidates may be selected based on the transform type of the neighboring block, and filtering may be performed on the reference sample using the same. That is, a predetermined filter may be selected in consideration of the transform type of the block to which the reference sample belongs. For example, as shown in FIG. 16, when the current block and the block adjacent to the left / lower left are blocks coded using DCT, and the block adjacent to the upper / right top is a block coded using DST, the left Filtering may be performed by applying a first intra filter to a reference sample adjacent to a lower left end, and filtering may be performed by applying a second intra filter to a reference sample adjacent to an upper / right end.

In units of a predetermined region, filters available for the corresponding region may be defined. Here, the predetermined area unit may be any one of a sequence, a picture, a slice, a block group (eg, coding tree unit row), and a block (eg, coding tree unit), and share one or more filters. Separate areas may be defined. The reference sample may be filtered using a filter mapped to the region to which the current block belongs.

For example, as illustrated in FIG. 17, filtering for a reference sample may be performed using different filters in units of CTU. In this case, in the sequence parameter set (SPS) or the picture parameter set (PPS), information indicating whether the sequence or picture uses the same filter, the type of filter used for each CTU, and the corresponding CTU among the available intra filter candidates An index or the like that specifies the filter used may be signaled.

The above-described intra filter may be applied in units of coding units. For example, filtering may be performed by applying a first intra filter or a second intra filter to reference samples around a coding unit.

In the case of using the directional prediction mode or the DC mode, there is a concern that image degradation occurs at the block boundary. On the other hand, in the planner mode, the image quality deterioration of the block boundary is relatively smaller than the prediction modes.

The planar prediction may be performed by generating the first prediction image in the horizontal direction and the second prediction image in the vertical direction using weighted reference samples, and then weighting the first prediction image and the second prediction image.

Here, the first prediction image may be generated based on reference samples adjacent to the current block placed in the horizontal direction of the sample to be predicted. For example, the first prediction image may be generated based on a weighted sum of reference samples placed in the horizontal direction of the prediction sample, and the weight applied to each reference sample may be a distance from the prediction sample or the size of the current block. It may be determined in consideration of. The samples located in the horizontal direction may include a left reference sample placed to the left of the predicted sample and a right reference sample placed to the right of the predicted sample. In this case, the right reference sample may be derived from an upper reference sample of the current block. For example, the right reference sample may be derived by copying a value of any one of the upper reference samples, or may be derived as a weighted sum or average value of the upper reference samples. Here, the upper reference sample is a reference sample positioned on the same vertical line as the right reference sample and may be a reference sample adjacent to the upper right corner of the current block. Alternatively, the position of the upper reference sample may be determined differently according to the position of the predicted sample.

The second prediction image may be generated based on reference samples adjacent to the current block in the vertical direction of the sample to be predicted. For example, the second prediction image may be generated based on a weighted sum of reference samples placed in a vertical direction of the sample to be predicted, and the weight applied to each reference sample may be a distance from the sample to be predicted or the size of the current block. It may be determined in consideration of. Samples located in the vertical direction may include an upper reference sample placed above the predicted sample and a lower reference sample placed below the predicted sample. In this case, the lower reference sample may be derived from the left reference sample of the current block. For example, the lower reference sample may be derived by copying a value of any one of the left reference samples, or may be derived as a weighted sum or an average value of the left reference samples, and the like. Here, the left reference sample is a reference sample located on the same horizontal line as the lower reference sample and may be a reference sample adjacent to the lower left corner of the current block. Alternatively, the position of the upper reference sample may be determined differently according to the position of the predicted sample.

As another example, a plurality of reference samples may be used to derive the right reference sample and the lower reference sample.

For example, both the right reference sample and the left reference sample of the current block may be used to derive the right reference sample or the lower reference sample. For example, at least one of the right reference sample or the lower reference sample may be determined as a weighted sum or average of the upper reference sample and the left reference sample of the current block.

Alternatively, the weighted sum or average of the upper reference sample and the left reference sample of the current block may be calculated, and then the right reference sample may be derived from the calculated value and the weighted sum or average of the upper reference sample. When the right reference sample is derived through the weighted operation of the calculated value and the upper reference sample, the size of the current block, the shape of the current block, the position of the right reference sample, or the distance between the right reference sample and the upper reference sample The weight can be determined.

In addition, after the weighted sum or average of the upper reference sample and the left reference sample of the current block is calculated, the lower reference sample may be derived from the calculated value and the weighted sum or average of the left reference sample. When deriving the right reference sample through the weighted operation of the calculated value and the left reference sample, the size of the current block, the shape of the current block, the position of the lower reference sample, or the distance between the lower reference sample and the left reference sample The weight can be determined.

The positions of the plurality of reference samples used to derive the right reference sample or the left reference sample may be fixed or may vary depending on the position of the sample to be predicted. For example, the upper reference sample has a fixed position with a reference sample adjacent to the upper right corner of the current block located on the same vertical line as the right reference sample, and the left reference sample is located on the same horizontal line as the lower reference sample. It may have a fixed position with a reference sample adjacent to the lower left corner of. Alternatively, when deriving a right reference sample, the upper reference sample may use a reference sample at a fixed position adjacent to the upper right corner of the current block, while the left reference sample may use a reference sample placed on the same horizontal line as the sample to be predicted. have. When deriving a lower reference sample, the left reference sample may use a reference sample at a fixed position adjacent to the lower left corner of the current block, while the upper reference sample may use a reference sample placed on the same vertical line as the sample to be predicted.

18 is a diagram illustrating an example of deriving a right reference sample or a lower reference sample using a plurality of reference samples. Assume that the current block is a block having a size of WxH.

Referring to FIG. 18A, first, a lower right reference sample P based on a weighted sum or average value of the upper reference samples P (W, −1) and the left reference samples P (−1, H) of the current block. (W, H) can be generated. Then, based on the lower right reference sample P (W, H) and the upper reference sample P (W, -1), the right reference sample P (W, y) for the target prediction sample (x, y) may be generated. have. For example, the right prediction sample P (W, y) may be calculated as a weighted sum or average value of the lower right reference sample P (W, H) and the upper reference sample P (W, -1). In addition, a lower reference sample P (x, H) for the target prediction sample (x, y) may be generated based on the lower right reference sample P (W, H) and the left reference sample P (-1, H). . For example, the lower reference sample P (x, H) may be calculated as a weighted sum or average of the lower right reference sample P (W, H) and the left reference sample P (-1, H).

As shown in FIG. 18B, when the right reference sample and the lower reference sample are generated, the first prediction sample P _h (x, y) and the second prediction sample for the sample to be predicted are generated using the generated reference sample. The prediction sample P _v (x, y) may be generated. In this case, the first prediction sample P _h (x, y) is generated based on the weighted sum of the left reference sample P (-1, y) and the right reference sample P (W, y), and the second prediction sample Pv (x , y) may be generated based on a weighted sum of the upper reference sample P (x, -1) and the lower reference sample P (x, H).

The positions of the reference samples used to generate the first prediction image and the second prediction image may vary depending on the size or shape of the current block. That is, according to the size or shape of the current block, the position of the upper reference sample or the left reference sample used to derive the right reference sample or the lower reference sample may vary.

For example, when the current block is a square block of size N × N, the right reference sample may be derived from P (N, −1) and the lower reference sample may be derived from P (−1, N). Alternatively, the right reference sample and the lower reference sample may be derived based on at least one of weighted sum, average, minimum or maximum value of P (N, -1) and P (-1, N). On the other hand, when the current block is non-square, according to the shape of the current block, the position of the reference sample used to derive the right reference sample and the lower reference sample may be determined differently.

As in the example shown in FIG. 19, when the current block is an (N / 2) × N non-square block, a right reference sample is derived based on the upper reference sample P (N / 2, -1), The lower reference sample can be derived based on the left reference sample P (-1, N).

Alternatively, derive the right reference sample or the lower reference sample based on at least one of the weighted sum, average, minimum, or maximum value of the upper reference sample P (N / 2, -1) and the left reference sample P (-1, N). You may. For example, a right reference sample may be derived from a weighted sum or average of P (N / 2, -1) and P (-1, N), or a right reference sample may be derived from a weighted sum or average between the calculated value and an upper reference sample. Can be induced. Alternatively, a lower reference sample may be derived by a weighted sum or mean of P (N / 2, -1) and P (-1, N), or a lower reference sample is obtained by a weighted sum or mean between the calculated value and the left reference sample. Can be induced.

On the other hand, as in the example shown in FIG. 20, when the current block is an Nx (N / 2) sized non-square block, the right reference sample is derived based on the upper reference sample P (N, -1), Based on the left reference sample P (-1, N / 2), the lower reference sample can be derived.

Alternatively, derive the right reference sample or the lower reference sample based on at least one of the weighted sum, the average, the minimum value, or the maximum value of the upper reference sample P (N, -1) and the left reference sample P (-1, N / 2). You may. For example, a right reference sample can be derived from a weighted sum or mean of P (N, -1) and P (-1, N / 2), or a right sum sample can be derived from a weighted sum or average between the calculated value and the upper reference sample. Can be induced. Or, derive a lower reference sample with a weighted sum or mean of P (N, -1) and P (-1, N / 2), or use a weighted sum or average between the calculated value and the left reference sample Can be induced.

That is, the lower reference sample is derived based on at least one of the lower left reference sample of the current block lying on the same horizontal line as the lower reference sample or the upper right reference sample of the current block lying on the same vertical line as the right reference sample, The reference sample may be derived based on at least one of the upper right reference sample of the current block lying on the same vertical line as the right reference sample or the lower left reference sample of the current block lying on the same horizontal line as the lower reference sample.

The first prediction image may be calculated based on weighted prediction of reference samples placed on the same horizontal line as the prediction target sample. Also, the second prediction image may be calculated based on weighted prediction of reference samples placed on the same vertical line as the sample to be predicted.

In addition to the above-described example, the first prediction image or the second prediction image may be generated using an average value, a minimum value, or a maximum value of the reference samples.

According to whether the sample to be predicted is included in a predetermined region of the current block, the size or shape of the current block, a method of deriving a reference sample differently or a method of deriving a first predicted image or a second predicted image Can be set differently. Specifically, according to the position of the prediction target sample, the number of reference samples or the position of the reference sample used to use the right or lower reference sample is differently determined, or used to derive the first prediction image or the second prediction image. The weight or the number of reference samples may be set differently.

For example, the right reference sample used when generating the first predictive image of the predicted samples included in the predetermined region is derived using only the upper reference sample, and the first predicted image of the predicted samples included outside the predetermined region. The right reference sample used when generating P may be derived based on a weighted sum or average of the top reference sample and the left reference sample.

For example, as in the example shown in FIG. 19, when the current block is a non-square block whose height is greater than the width, the right reference sample of the predicted sample at the position (x, y) included in a predetermined area within the current block is P. Can be derived from (N / 2, -1). On the other hand, the right reference sample of the predicted sample at the (x ', y') position included outside a predetermined area in the current block has a weighted sum or average value of P (N / 2, -1) and P (-1, N). Can be derived based on

Or, as in the example shown in FIG. 20, when the current block is a non-square block having a width greater than the height, the lower reference sample of the predicted sample at the position (x, y) included in the predetermined area of the current block is P. Can be derived from (-1, N / 2). On the other hand, the lower reference sample of the predicted sample at the (x ', y') position included outside the predetermined area in the current block has a weighted sum or average value of P (N, -1) and P (-1, N / 2). Can be derived based on

For example, the prediction target samples included in the predetermined region may generate the first prediction image or the second prediction image based on the weighted sum of the reference samples. On the other hand, the samples to be predicted outside the predetermined region may generate the first prediction image or the second prediction image using the average value, the minimum value, or the maximum value of the reference samples, or use only the first one of the predefined positions among the reference samples. A prediction image or a second prediction image may be generated. For example, as in the example illustrated in FIG. 19, when the current block is a non-square block having a height greater than the width, the predicted sample at the position (x, y) included in a predetermined area within the current block is P (N). The first prediction image may be generated using only one of a right reference sample P (N / 2, y) or a left reference sample at a P (-1, y) position derived from / 2, -1). On the other hand, the sample to be predicted at the position (x ', y') not included in the predetermined region includes the right reference samples P (N / 2, y ') and P (derived from P (N / 2, -1). The first prediction image may be generated based on a weighted sum or an average of the reference samples at the position of −1, y ′).

Or, as in the example shown in FIG. 20, when the current block is a non-square block having a width greater than the height, the sample to be predicted at the position (x, y) included in the predetermined area of the current block is P (-1). , N / 2) may generate the second prediction image using only one of the lower reference samples P (x, N / 2) or the upper reference samples at the P (x, -1) positions. On the other hand, the predicted sample at the position (x ', y') that is not included in the predetermined region includes the lower reference samples P (x ', N / 2) and P (derived from P (-1, N / 2). The second prediction image may be generated based on a weighted sum or an average of the reference samples at the position of −1, y ′).

In the above-described embodiment, the predetermined region or an outer region of the predetermined region may include a residual region except for a sample located at the boundary of the current block. The boundary of the current block may include at least one of a left boundary, a right boundary, an upper boundary, or a lower boundary. In addition, the number or positions of the boundaries included in the predetermined region or outside the predetermined region may be set differently according to the shape of the current block.

The final prediction image under the planner mode may be derived based on a weighted sum, an average, a minimum value, or a maximum value of the first prediction image and the second prediction image.

For example, Equation 9 below illustrates an example of generating a final predicted image P based on a weighted sum of the first predicted image P _h and the second predicted image P _v .

In Equation 9, the prediction weight w may be different according to the shape, size of the current block, or the position of the sample to be predicted.

For example, the prediction weight w may be derived in consideration of the width of the current block, the height of the current block, or the width-height ratio. When the current block is a non-square block having a width greater than the height, w may be set to give more weight to the first prediction image. On the other hand, if the current block is a non-square block whose height is greater than the width, w may be set to give more weight to the second prediction image.

As an example, when the current block is square, the prediction weight w may have a value of 1/2. On the other hand, if the current block is a non-square block whose height is greater than the width (e.g. (N / 2) xN), the prediction weight w is set to 1/4, and the current block is a non-square block whose width is greater than the height (e.g. , Nx (N / 2)), the prediction weight w may be set to 3/4.

First, a residual coefficient of the current block may be obtained (S2110). The decoder may acquire the residual coefficients through the coefficient scanning method. For example, the decoder may perform coefficient scanning using diagonal scan, zigzag scan, up-write scan, vertical scan, or horizontal scan, and as a result, obtain a residual coefficient in the form of a two-dimensional block.

Inverse quantization may be performed on the residual coefficient of the current block (S2120).

It may be determined whether to inverse transform the skipped inverse quantized residual coefficient of the current block (S2130). In detail, the decoder may determine whether to skip an inverse transform in at least one of the horizontal direction and the vertical direction of the current block. When it is determined to apply an inverse transform to at least one of a vertical or horizontal direction of the current block, a residual sample of the current block may be obtained by inversely transforming an inverse quantized residual coefficient of the current block (S2140). Here, the inverse transform may be performed using at least one of DCT, DST, or KLT.

If the inverse transform is skipped in both the horizontal and vertical directions of the current block, the inverse transform is not performed in the horizontal and vertical directions of the current block. In this case, the residual quantized residual coefficient may be scaled to a preset value to obtain a residual sample of the current block (S2150).

Omitting the inverse transform in the horizontal direction means performing the inverse transform in the vertical direction without performing the inverse transform in the horizontal direction. In this case, scaling may be performed in the horizontal direction.

Omitting the inverse transform in the vertical direction means not performing the inverse transform in the vertical direction but performing the inverse transform in the horizontal direction. In this case, scaling may be performed in the vertical direction.

According to the partition type of the current block, it may be determined whether an inverse transform skip technique may be used for the current block. For example, when the current block is generated through binary tree-based partitioning, the inverse transform skip technique may not be used for the current block. Accordingly, when the current block is generated through binary tree-based partitioning, a residual sample of the current block may be obtained by inversely transforming the current block. In addition, when the current block is generated through binary tree-based partitioning, encoding / decoding of information (eg, transform_skip_flag) indicating whether an inverse transform is skipped may be omitted.

Alternatively, when the current block is generated through binary tree based partitioning, the inverse transform skip technique may be limited to only at least one of the horizontal direction and the vertical direction. Here, the direction in which the inverse transform skip technique is limited may be determined based on information decoded from the bitstream or adaptively determined based on at least one of the size of the current block, the shape of the current block, or the intra prediction mode of the current block. have.

For example, when the current block is a non-square block having a width greater than the height, the inverse skip skip technique may be allowed only in the vertical direction, and the use of the inverse skip skip technique may be restricted in the horizontal direction. That is, when the current block is 2N × N, inverse transform may be performed in the horizontal direction of the current block, and inverse transform may be selectively performed in the vertical direction.

On the other hand, when the height of the current block is a non-square block larger than the width, the inverse skip skip technique can be allowed only in the horizontal direction, and the use of the inverse skip skip technique can be restricted in the vertical direction. That is, when the current block is Nx2N, inverse transform may be performed in the vertical direction of the current block, and inverse transform may be selectively performed in the horizontal direction.

In contrast to the above example, if the current block is a non-square block with a width greater than its height, the inverse skipping scheme is allowed only for the horizontal direction; if the current block is a non-square block with a height greater than the width, an inverse transform for the vertical direction only The skip technique may be allowed.

Information on whether to skip the inverse transform in the horizontal direction or information indicating whether to skip the inverse transform in the vertical direction may be signaled through the bitstream. For example, the information indicating whether to skip the inverse transform in the horizontal direction is a 1-bit flag, 'hor_transform_skip_flag', and the information indicating whether to skip the inverse transform in the vertical direction is a 1-bit flag, and the 'ver_transform_skip_flag' Can be '. The encoder may encode at least one of 'hor_transform_skip_flag' or 'ver_transform_skip_flag' according to the shape of the current block. In addition, the decoder may determine whether an inverse transform in the horizontal direction or the vertical direction is skipped using at least one of 'hor_transform_skip_flag' or 'ver_transform_skip_flag'.

Depending on the division type of the current block, in either direction, the inverse transform may be set to be omitted. For example, when the current block is generated through a binary tree based partitioning, an inverse transform in the horizontal direction or the vertical direction may be omitted. That is, if the current block is generated by partitioning based on a binary tree, the horizontal or vertical direction with respect to the current block may be performed without encoding / decoding of information indicating whether the inverse transform of the current block is skipped (for example, transform_skip_flag, hor_transform_skip_flag, ver_transform_skip_flag). It may be determined to skip the inverse transformation for at least one of the following.

Although the above-described embodiments are described based on a series of steps or flowcharts, this does not limit the time-series order of the invention and may be performed simultaneously or in a different order as necessary. In addition, in the above-described embodiment, each component (for example, a unit, a module, etc.) constituting the block diagram may be implemented as a hardware device or software, and a plurality of components are combined into one hardware device or software. It may be implemented. The above-described embodiments may be implemented in the form of program instructions that may be executed by various computer components, and may be recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs, DVDs, and magneto-optical media such as floptical disks. media), and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The hardware device may be configured to operate as one or more software modules to perform the process according to the invention, and vice versa.

The present invention can be applied to an electronic device capable of encoding / decoding an image.

Claims

Deriving a reference sample for the current block;

Determining an intra prediction mode of the current block; And

Using the reference sample and the intra prediction mode, obtaining a prediction sample for the current block,

When the intra prediction mode is a planner mode, the prediction sample includes a first prediction sample using at least one reference sample placed on the same horizontal line as the prediction target sample and at least one reference placed on the same vertical line as the prediction target sample. And based on the second prediction sample using the sample.
According to claim 1,

The reference sample comprises a top reference sample and a left reference sample adjacent to the current block,

The first prediction sample is generated using at least one of the right reference sample derived based on the left reference sample and the top reference sample,

The second prediction sample is generated using at least one of the lower reference sample derived based on the upper reference sample and the left reference sample.
The method of claim 2,

The position of the top reference sample used to derive the right reference sample, or the position of the left reference sample used to derive the bottom reference sample is variably determined according to the size or shape of the current block. A video decoding method.
The method of claim 2,

The first prediction sample is generated based on a weighted sum between the left reference sample and the right reference sample, and the second prediction sample is generated based on a weighted sum between the top reference sample and the bottom reference sample. A video decoding method.
The method of claim 2,

The number of reference samples used to derive the first predictive sample or the second predictive sample is differently determined according to the position of the predicted sample.
According to claim 1,

And the prediction sample is generated based on a weighted sum of the first prediction sample and the second prediction sample.
The method of claim 6,

The weights of the first prediction sample and the second prediction sample are differently determined according to the shape of the current block.
Deriving a reference sample for the current block;

Determining an intra prediction mode of the current block; And

Using the reference sample and the intra prediction mode, obtaining a prediction sample for the current block,

When the intra prediction mode is a planner mode, the prediction sample includes a first prediction sample using at least one reference sample placed on the same horizontal line as the prediction target sample and at least one reference placed on the same vertical line as the prediction target sample. And based on the second prediction sample using the sample.
The method of claim 8,

The reference sample comprises a top reference sample and a left reference sample adjacent to the current block,

The first prediction sample is generated using at least one of the right reference sample derived based on the left reference sample and the top reference sample,

The second prediction sample is generated using at least one of the lower reference sample derived based on the upper reference sample and the left reference sample.
The method of claim 9,

The position of the top reference sample used to derive the right reference sample, or the position of the left reference sample used to derive the bottom reference sample is variably determined according to the size or shape of the current block. The video encoding method.
The method of claim 9,

The first prediction sample is generated based on a weighted sum between the left reference sample and the right reference sample, and the second prediction sample is generated based on a weighted sum between the top reference sample and the bottom reference sample. A video encoding method.
The method of claim 9,

The number of reference samples used to derive the first predictive sample or the second predictive sample is differently determined according to the position of the predicted sample.
The method of claim 8,

The prediction sample is generated based on a weighted sum of the first prediction sample and the second prediction sample.
The method of claim 13,

The weights for the first prediction sample and the second prediction sample are differently determined according to the shape of the current block.
An intra prediction unit for deriving a reference sample for a current block, determining an intra prediction mode of the current block, and obtaining a prediction sample for the current block by using the reference sample and the intra prediction mode,

When the intra prediction mode is a planner mode, the intra prediction unit may include a first prediction sample using at least one reference sample placed on the same horizontal line as the prediction target sample and at least one reference placed on the same vertical line as the prediction target sample. And generating the prediction sample based on the second prediction sample using the sample.